1. Field of the Invention
The present invention relates generally to self-fusing, or self-amalgamating, compositions. More particularly, the invention relates to rubber blend compositions, preferably formed into tapes, which, after being elongated and, for example, wrapped around a substrate, fuse together to form a continuous layer. In preferred aspects of the invention, the layer advantageously functions as an electrical insulator and/or waterproof cover.
2. Discussion of Related Art
Dimensionally recoverable, or shrinkable, articles such as tubular and wraparound sleeves are known for use in enclosing or covering elongate substrates such as pipes or cables and, in particular, cable joints or splices. Such sleeves are useful for providing environmental and corrosion protection, and for providing additional structural integrity, to joints, fittings and welds by which pipes, cables, conduits and other elongated members are joined. One well-known type of material for forming such protective sleeves is a dimensionally heat recoverable, or heat shrinkable, material, which, when applied over a joint and subjected to heat, shrinks tightly into contact with the substrate.
Dimensionally recoverable articles which do not require heat to effect recovery are also known. As one example, there are known articles which are formed of an elastomeric sheet or tube held in an expanded state by a restraining means which can be removed or separated from the elastomeric member to permit it to recover to the unexpanded state. Contact adhesives, or other adhesives may be used to seal such a recovered article to a substrate.
Another type of shrinkable tubing material which does riot require heating is a shrinkable protective tubing which has been dilated with chemicals to bring the same to a dilated or expanded state. This type of tubing remains dilated or expanded so long as it is kept out of contact with air; however, once the tubing contacts ambient air, it shrinks back to its initial size without the application of heat.
As an alternative to pre-formed, shrinkable sleeves as described above, there are known in the prior art thin sheets or tapes which may be layered over an article in a wrapping action to provide protection from the environment or to provide structural integrity to, for example, a joint or splice. In pipe wrapping operations, for example, a separate adhesive layer is generally used to achieve adhesion to the substrate and of the overlapping layers to each other. In electrical applications such as cable splicing, the tape is wrapped, usually spirally, around an electric cable.
Attempts have also been made to produce self-bonding tapes from compounds containing chlorosulfonated and chlorinated polyethylene and various compounding ingredients such as fillers, plasticizers and tackifiers. An advantage of such a product is that it avoids the use of adhesives, which are difficult and expensive to handle and apply to a tape. These self-bonding tapes, however, were found to be tacky in the relaxed state, rendering them difficult to handle.
Various self-bonding tapes have been previously described, for example, in U.S. Pat. No. 4,788,245 to Anderson; U.S. Pat. No. 4,925,715 to Sato; and U.S. Pat. No. 5,268,051 to Kent et al. In the '245 patent, there is disclosed a composition comprising specific ratios of the following components: a rubber component selected from the group consisting of conjugated diene butyl rubber and halobutyl rubber; a polyisobutylene tackifier; a polyethylene; carbon black; and an antioxidant.
The Sato patent discloses a tension-wound, linerless roll of tape comprising in specifically described ratios (I) a polymer mixture selected from the group consisting of (a) a mixture of a polymer of ethylene having a density of from about 0.945 to about 0.965 grams/cm.sup.3 with an elastomeric polymer, (b) a mixture of a linear low density polymer of ethylene having a density of from about 0.91 to about 0.94 grams/cm.sup.3 with an elastomeric polymer, and (c) a mixture of isotactic polypropylene with an elastomeric polymer, said elastomeric polymer consisting of an isobutylene isoprene polymer and one or more polymers selected from (i) natural rubber, (ii) a homopolymer of isobutylene having a molecular weight from about 50,000 to about 100,000, and (iii) a polymer of ethylene and propylene containing from about 50 to about 65 percent by weight ethylene; and (II) from 0.4 to 4 parts (per 100 parts of said polymer mixture) of fatty amide anti-blocking agent.
In the Kent et al patent there is disclosed a tape comprising in specifically described ratios a raw polymer mixture of (a) a chlorosulfonated polyethylene rubber; (b) a thermoplastic polymer selected from the group consisting of (i) a polymer of ethylene having a density of from about 0.945 to about 0.965 gm/cm.sup.3 (ii) a linear low density polymer of ethylene having a density of from about 0.91 to about 0.94 gm/cm.sup.3, and (iii) isotactic polypropylene; (c) a chlorinated polyethylene rubber; (d) an elastomeric polymer selected from the group consisting of (i) isobutylene-isoprene polymer, (ii) homopolymer of isobutylene having a Staudinger molecular weight from about 30,000 to about 100,000 and (iii) a polymer of ethylene and propylene containing from about 50 to about 65 percent by weight of ethylene for a total of 100 parts of (a), (b), (c) and (d); and (e) from about 0.5 to about 20 parts per 100 parts of (a), (b), (c) and (d) of one or more filler or pigment.
The compositions disclosed in these patents have the same disadvantage, however, that they all comprise in significant proportions plastic materials such as polypropylene, polyethylene, linear low density ethylene polymer and/or isotactic polypropylene. While the plastic compositions therein improve the processability of the overall composition, the plastic components and the rubber components are not highly cohesive and, therefore, after the ingredients are blended, the blend must be crosslinked to produce a final composition having adequate physical properties. For example, the Anderson patent teaches that a blend made in accordance therewith must be vulcanized by radiation. Radiation generation, however, is very expensive, thus necessitating a large capital investment to make self-amalgamating materials in accordance with the Anderson patent. An additional disadvantage of blends comprising plastic materials, is that the required crosslinking creates a significant likelihood of oxidation. The crosslinks in such a composition are points for oxygen to attack, thereby resulting in oxidation of the polymers. Additionally, the presence of plastics in these materials makes necessary a significant amount of tackifier. The amount of tackifier needed increases as a function of the proportion of plastic components in the material.
These and other problems associated with self-fusing, or self-amalgamating compositions disclosed in the prior art are overcome by the present invention, which teaches a rubber blend, in which the blend of starting materials need not be crosslinked prior to use. Thus, inventive compositions are significantly more resistant to degradation than self-fusing compositions taught in the prior art, are significantly less costly to produce and exhibit a significantly longer useful life. Further, inventive compositions exhibit excellent physical properties, such as elongation, tensile strength, resistance to ozone, sunlight, UV, moisture and salt spray, volume resistivity and dielectric properties. Inventive compositions are useful across a wide range of temperatures, retaining their advantageous properties at temperatures as low as, for example, -40.degree. F., and as high as, for example, 250.degree. F. Thus, the invention provides compositions and methods which satisfy a long-felt need in the prior art for a self-fusing material which may be economically made and which exhibits excellent physical properties.